A display device using a liquid crystal compound is widely utilized for a display of a watch, a calculator, a word processor and so forth. The display devices utilize characteristics of the liquid crystal compound, such as optical anisotropy and dielectric anisotropy.
A liquid crystal phase includes a nematic liquid crystal phase, a smectic liquid crystal phase and a cholesteric liquid crystal phase, and the nematic liquid crystal phase is most widely utilized. Specific examples of display modes include a dynamic scattering (DS) mode, a deformation of aligned phases (DAP) mode, a guest/host (GH) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, a thin film transistor (TFT) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, an optical compensation bend (OCB) mode, an in-plane switching (IPS) mode and a polymer sustained alignment (PSA) mode.
For the liquid crystal compound used in the display modes, characteristics such as having a liquid crystal phase in a wide temperature range centering on room temperature, being sufficiently stable under conditions in which the display device is used, and having sufficient characteristics for driving the display device are required. However, no single compound meeting the requirements is found at present.
Therefore, a liquid crystal composition meeting the requirements is prepared by mixing several kinds to several tens kinds of liquid crystal compounds. The requirements desired for the liquid crystal compound constituting the liquid crystal composition are as described below.
The requirements include:
(1) high stability to heat, light and so forth;
(2) high clearing point (clearing point: phase transition temperature between the liquid crystal phase and an isotropic phase);
(3) low minimum temperature of a liquid crystal phase such as the nematic phase and the smectic phase, particularly, a low minimum temperature of the nematic phase;
(4) suitable optical anisotropy;
(5) large dielectric anisotropy;
(6) suitable elastic constant; and
(7) excellent solubility in other liquid crystal compounds
As a display mode for overcoming narrowness of viewing angle being a biggest problem of the liquid crystal display device, among the display modes, the modes such as the IPS mode, the VA mode, the OCB mode and the PSA mode attract attention in recent years. Among the liquid crystal display devices according to the modes, in particular, the liquid crystal display device according to the IPS mode or the VA mode has a wide viewing angle and also an excellent responsiveness to further obtain a high contrast display, and thus is actively developed. Features of the liquid crystal composition used for the liquid crystal display devices according the display modes are in a negative value of dielectric anisotropy. Further, a liquid crystal composition having a large negative value of dielectric anisotropy is known to allow a decrease of driving voltage of the liquid crystal device including the liquid crystal composition (see Non-patent literature No. 1). Therefore, the liquid crystal compound being a constituent of the liquid crystal composition is also required to have a larger negative value of dielectric anisotropy.
An attempt has been made so far for increasing an absolute value of negative dielectric anisotropy in a compound having a 2,3-difluorophenylene skeleton. For example, a compound prepared by introducing a tetrahydropyran-2,5-diyl skeleton into a compound having a 2,3-difluorophenylene skeleton is reported (Patent literature No. 1). Compound (b) shows a large negative dielectric anisotropy in comparison with compound (a).

Furthermore, as a compound showing a negative dielectric anisotropy, compound (15) having a 2,3-difluoro-1,4-phenylene skeleton is generally known (Non-patent literature No. 3). In order to further increase an absolute value of negative dielectric anisotropy, compound (16) prepared by bonding trifluoromethyl on a lateral position of a molecule; and compound (17), compound (18) and compound (19) each prepared by bonding difluoromethyl on a lateral position of a molecule have been reported (Patent literature No. 2, Non-patent literature No. 2, Non-patent literature No. 3, Patent literature No. 3 and Patent literature No. 4).

In order to decrease the driving voltage of the liquid crystal display device according to the IPS mode, the VA mode or the like, a liquid crystal compound having a further large negative value of dielectric anisotropy, a liquid crystal composition containing the compound and a liquid crystal display device including the liquid crystal composition are desired.